Generally, distribution of video signals has been carried out using a coaxial cable connected communication network. However, due to the high cost and minimal signal quality of such a distribution network, attempts have been made to provide an alternative approach to distributing video signals. For example, telephone lines have been suggested as a physical structure for implementing video signal distribution. However, systems using the public switched telephone network (PSTN) are often bandwidth limited, providing generally only still frame or video conferencing capabilities. In addition, because telephone system carriers only typically use the PSTN for connectivity between subscribers, the PSTN does not provide any capability for dynamic routing digitized video without the use of dedicated leased, wide bandwidth circuits. Telephone line based systems also fail to provide acceptable VCR type functional control over the distribution of video programming.
On the other hand, an enhanced public switched telephone network does provide the capability distributing video on demand to subscribers over the PSTN. In such an arrangement, a menu of video programming information is made accessible at a subscriber's premises. A subscriber may transmit ordering information via the PSTN to available independent video information providers. Video programming can then be accessed and transmitted to the subscriber directly from a video information provider or through a central office (CO) serving the subscriber. The video information provider is suitably arranged to transmit coded digital video data over wideband PSTN connected to the CO. The video data may be buffered at the central office for transmission over a plain old telephone service (POTS) line to the subscriber. Subscribers may use either a standard telephone or a dedicated control device located at a television set to order the video programming.
The central office can be connected to the various subscribers for transmission of video data using an asymmetrical digital subscriber line (ADSL) system. In such an arrangement, multiple ADSL interface units would be deployed to perform multiplexing of digital video information with voice information to be transmitted to the subscriber. The ADSL units would also provide support for transmission of one or more reverse control channels from the subscriber to the central office. The ADSL interface units are typically located at the central office and the subscriber location and are operative to combine video information together with bidirectional signalling and POTS for transmission over an ordinary telephone wiring plant.
However, known ADSL type transmission systems have not proven to be fully satisfactory. When environmental interference situations arise, ADSL transmission is more sensitive than POTS. As transmission distances over copper wire pairs exceed 18,000 feet, the signal quality of ADSL signals becomes seriously degraded. Thus, a need exists for a video signal distribution system which overcomes the above-noted problems.